Written by :
Luciano Mastronardi, Raffaelino Roperto, Guglielmo Cacciotti, Maria Pia Tonelli, Franco Caputi
Department of Neurosurgery; San Filippo Neri Hospital, Rome, Italy
Introduction: The elimination of motion produced by spinal fusion may have potential consequences, overloading the juxtaposed spinal motion segments and leading to the appearance of degenerative changes. Degeneration of the segments adjacent to instrumented levels has become a topic of increasing interest in the literature over the last years. In order to prevent degenerative disc changes at the adjacent segments to a fused level, several techniques have been developed, one of them is the pedicle screw fixation with flexible bars (semi-rigid dynamic rods).
Methods: Twenty consecutive patients with degenerative spinal diseases received posterior lumbar spinal fusion with flexible bars. Preoperatively, 10 patients had low back pain for segmental lumbar instability instability, 6 had severe lumbar stenosis with degenerative listhesis, 2 had stenosis with instability, 1 had a mild listesis with instability, and 1 had a traumatic fracture of L1.
In six cases a severe osteoporosis was also detected, with a pre-operative mean T-score of -3.1 on DEXA BMD examination. In 14 cases the spinal fixation was performed using pedicle screws and flexible bars of three different brands (Isobar Evolution/Scient’x-Alphatec; Flex plus/Spinevision; Blackstone). In the 6 patients with severe osteoporosis titanium expandable screws (Osseoscrew, Scient’x-Alphatec) with standard titanium rods were used; in ten cases the patients performed a posterior fusion using Isobar Evolution (semi-rigid dynamic rods). Patients were observed for a follow up period ranging from 3 to 45 months.Outcome measures included screw loosening, Visual Analogue Scale, Oswestry Disability Index, and complications.
Results: At a median follow up of 18 months, the VAS and ODI were markedly improved in 18 cases.There were two cases with recurrent low back pain (2 osteoporotic patients with stenosis and lysthesis) and three cases of CSF leakage in patients with severe stenosis and lysthesis, not related to the device, which healed after corresponding treatment. There were no instances of screw loosening or pull-out of the expandable screws, and the screw-bone interface was good. In patients with dynamic fixation, we prevented until now degenerative lesions above the fixated segment. On plain radiographs and spinal CT, there were no signs of radiolucency around the pedicle screws. Dynamic x-rays, revealed non- motion of the screws and no movement between the fused vertebral segments. Expandable screw breakage did not occur in any patients. Implant failure did not occur in any study patients.
Conclusions: In our series, we observed good clinical outcomes in the treatment of different lumbar diseases with a posterior flexible stabilization. The raise of intradiscal pressure at the adjacent segment consecutive to a rigid instrumented segment can be reduced when the rigid construct is augmented with a flexible stabilization device, using semi-rigid dynamic rods. These constructs might have a possible protecting role preventing the occurrence of degenerative disc changes at the adjacent segment. Augmentation with a titanium expandable screws may represent an advisable solution in patients with documented severe osteoporosis.